The present disclosure relates to a light-emitting device, and a display apparatus and an illumination apparatus using the light-emitting device.
Organic electroluminescence devices (hereinafter, referred to as “organic EL devices”) have attracted attention as light-emitting devices capable of emitting high luminance light at a low voltage DC and have been actively researched and developed. An organic EL device has a structure in which an organic layer including a light-emitting layer which has a thickness of, typically, several tens of nanometers to several hundreds of nanometers is interposed between a reflective electrode and a translucent electrode. Light emitted from the light-emitting layer is extracted to the outside, and an attempt to improve the luminous efficiency of the organic EL device using light interference in a device structure has been made. In addition, as a device capable of improving luminous efficiency and emission lifetime, an organic EL device having a stacked structure (so-called a tandem structure) in which plural light-emitting layers are stacked through a connection layer so as to connect the light-emitting layers to each other in series is well-known, and an arbitrary number of light-emitting layers can be stacked. For example, by stacking a blue light-emitting layer which emits blue light, a green light-emitting layer which emits green light, and a red light-emitting layer which emits red light, white light can be emitted as a combined light of blue light, green light, and red light.
An organic EL device having such a configuration is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2011-159432. The organic EL device disclosed in Japanese Unexamined Patent Application Publication No. 2011-159432 includes:
an organic layer which is interposed between a first electrode and a second electrode and in which a first light-emitting layer and a second light-emitting layer emitting light of single colors or two or more different colors in a visible wavelength region are sequentially included at mutually separated positions in that order in a direction from the first electrode to the second electrode;
a first reflective interface which is provided on the side of the first electrode so as to reflect light emitted from the first light-emitting layer and the second light-emitting layer to be emitted from the side of the second electrode; and
a second reflective interface and a third reflective interface which are sequentially provided on the side of the second electrode at mutually separated positions in that order in a direction from the first electrode to the second electrode, in which when an optical distance between the first reflective interface and a luminescent center of the first light-emitting layer is L11, an optical distance between the first reflective interface and a luminescent center of the second light-emitting layer is L21, an optical distance between the luminescent center of the first light-emitting layer and the second reflective interface is L12, an optical distance between the luminescent center of the second light-emitting layer and the second reflective interface is L22, an optical distance between the luminescent center of the first light-emitting layer and the third reflective interface is L13, an optical distance between the luminescent center of the second light-emitting layer and the third reflective interface is L23, a central wavelength of an emission spectrum of the first light-emitting layer is λ1, and a central wavelength of an emission spectrum of the second light-emitting layer is λ2, L11, L21, L12, L22, L13, and L23 are chosen so as to satisfy all the expressions (1) to (6) and at least one of the expressions (7) and (8).2L11/λ11+ϕ1/2π=0  (1)2L21/λ21+ϕ1/2π=n (where n≥1)  (2)λ1−150<λ11<λ1+80  (3)λ2−30<λ21<λ2+80  (4)2L12/λ12+ϕ2/2π=m′+½ and 2L13/λ13+ϕ3/2π=m″; or 2L12/λ12+ϕ2/2π=m′ and 2L13/λ13+ϕ3/2π=m″+½  (5)2L22/λ22+ϕ2/2π=n′+½ and 2L23/λ23+ϕ3/2π=n″; 2L22/λ22+ϕ2/2π=n′ and 2L23/λ23+ϕ3/2π=n″+½; or2L22/λ22+ϕ2/2π=n′+½ and 2L23/λ23+ϕ3/2π=n″+½  (6)λ22<λ2−15 or λ23>λ2+15  (7)λ23<λ2−15 or λ22>λ2+15  (8)
where m′, m″, n, n′, and n″ are integers,
λ1, λ2, λ11, λ21, λ12, λ22, λ13, and λ23 are in units of nm,
ϕ1 is a phase shift occurring when light of each wavelength is reflected by the first reflective interface,
ϕ2 is a phase shift occurring when light of each wavelength is reflected by the second reflective interface, and
ϕ3 is a phase shift occurring when light of each wavelength is reflected by the third reflective interface.
By adopting such a configuration, it is possible to realize a light-emitting device capable of effectively extracting light in a wide wavelength region and greatly reducing a viewing-angle dependency of luminance and chromaticity with respect to light of a single color or a combined color of two or more different colors in the visible wavelength region.
In addition, the viewing angle characteristics can be improved by additionally providing a fourth reflective interface in addition to the first, second, and third reflective interfaces. In the fourth reflective interface, depending on the stacking order of two light-emitting layers, a positional condition of the fourth reflective interface under which light rays are reinforced or weakened exists.